Free-Roaming Cats Are Top Bird-Killers, Researchers Say

By Andrew Pollack -
Jan 30, 2013

Free-roaming cats, including
domestic pets allowed out of the house, kill as many as
3.7 billion birds in the U.S. each year, far more than previous
estimates, according to a report from wildlife researchers.

Feral cats and their prowling domestic cousins also
dispatched as many as 20.7 billion small mammals such as rabbits
and squirrels, making them more deadly to wildlife than cars,
buildings, windmills or other objects, wrote Scott R. Loss, a
scientist at the Smithsonian Conservation Biology Institute in
Washington and an author of the report.

The findings suggest that free-ranging cats are “likely
the single greatest source” of so-called anthropogenic
mortality for U.S. birds and mammals, Loss wrote in the study
conducted with colleagues at the Smithsonian and the U.S. Fish
and Wildlife Service and published yesterday in the journal
Nature Communications.

“Our estimates should alert policy makers and the general
public about the large magnitude of wildlife mortality caused by
free-ranging cats,” the authors wrote.

The report estimates that cats kill 1.4 billion to 3.7
billion birds annually and 6.9 billion to 20.7 billion mammals,
including mice, shrews, voles, squirrels and rabbits. Previous
research estimated bird deaths from cats in the “hundreds of
millions” and “no large-scale mortality estimates exist for
mammals,” the authors wrote.

The scientists derived their estimates using a mathematical
model after analyzing previous research including small local
studies of cat-wildlife contacts and various figures for the
owned and wild cat population in the U.S.

“No precise estimate of the un-owned cat population exists
in the U.S. because obtaining such an estimate is cost-
prohibitive and feral, un-owned cats are wary of humans and tend
to be solitary outside of urban area,” according to the report.